Conventionally, various self-moving robots have been developed, some of which have wheels, others of which have caterpillars, and still others of which have leg sections. As a walking robot having leg sections, multi-legged walking robots such as a biped or two-legged robot, a three-legged robot, a quadruped or four-legged robot, a six-legged robot, etc., have been developed. In particular, various types of quadruped walking robots have recently been developed in view of high stability in walking motions, and by a reason that these robots are manufactured mimicking a four-legged animal such as, for example, a dog, a cat, etc.
A walking motion of the quadruped walking robot is carried out in such a manner that, for example, in a state where the tip ends of the three legged sections are grounded to support the weight of a main body portion, etc., the remaining one leg is grounded after being moved to another point of the ground using the leg as a free or idle leg, and walking and movement are executed with the weight of a robot supported, by changing over such grounding legs and an idle leg at the respective leg sections by turns.
As such a quadruped walking robot, Patent Document 1 refers to a multi-legged walking robot in which a plurality of legs or leg sections are provided for the sides of the main body portion, and describes a construction in which the respective legs are provided with the first turning axis, the second turning axis and the third turning axis. A leg of the quadruped walking robot according to Patent Document 1 is composed of a first unit disposed at the side of the main body portion, a second unit attached to the first unit via a first joint portion, and a third unit attached to the second unit via a second joint portion, wherein the first joint portion is composed of a first turning axis having its axial direction in the direction parallel to the side of the main body portion, and a second turning axis having its axial direction in the perpendicular direction to the side of the main body portion, and the second joint portion is composed of a third turning axis parallel to the second turning axis.
Patent Document 1: Japanese Published Unexamined Patent Application No. 2002-11679